I believe this was answered on one of the other forums. From 1987-1989 Buck was manufacturing bayonets for Phrobis' military contract. Those bayonets were marked with the Phrobis information on the left ricasso. The right ricasso was blank. At the same time, Buck was manufacturing bayonets for the commercial market. These had the Phrobis markings on the left ricasso and Buck markings on the right ricasso. In 1990, after the completion of the military contract, Buck continued to manufacture bayonets for the commercial market. These bayonets had the Buck markings on the left ricasso and the right ricasso was blank. This continued through 1997 when Buck ceased manufacture of the M9 bayonet.